to my understanding, T-tests are best to suit the case when the main interest is in mean differences on a single dependent variable between two groups. but will use MANOVA if your evaluation is in multiple group situations like more than two, and the interest here is in simultaneously assessing the psychological intervention's impact on multiple outcome measures.

The concept of disincentives being the biggest factor in human behavior is a matter of perspective and can vary depending on the context. It is not universally agreed upon, as different theories and schools of thought exist regarding human behavior.

One perspective that supports the idea of disincentives as a significant factor in human behavior is rooted in classical economics. Classical economists argue that individuals are primarily motivated by self-interest and respond to incentives. Therefore, they believe that disincentives, such as penalties or punishments, can deter certain behaviors or reduce motivation.

Additionally, behaviorists, like B.F. Skinner, emphasize the role of rewards and punishments in shaping human behavior. They argue that individuals learn through consequences, with punishments acting as disincentives that discourage undesirable behaviors.

However, it is important to note that there are other theories and factors that also influence human behavior. For instance, human behavior can be motivated by intrinsic factors such as personal values, social norms, and psychological needs. Other economic theories, like behavioral economics, consider cognitive biases and social influences as significant factors that shape behavior.

In summary, while some perspectives and theories emphasize the role of disincentives in human behavior, it is not universally agreed upon. Human behavior is complex and influenced by a multitude of factors, including both incentives and disincentives, as well as intrinsic motivations and social influences.

Your average human is theory-lite when it comes to making decisions of the "free" variety, generally speaking (Haynes 2022). This extends to most aspects of our dealings, including finances. The most extreme form it is people who engage in zero-sum thinking (zero-sum bias).

As an ex-federally licensed banker I can tell you that prior the Dodd-Franklin Act that regulated the housing market, people applied for loans that required no income, no verification, no job, no assets, nothing, and got approved.

The equivalent of this would similar concept of Hanna Arendt's notion of the Banality of Evil, the Banality of Spending. For most it doesn't even register, so disincentives are needed to shape up behavior. But the issue is multi-faceted, for sure.